Species composition and invasion risks of alien ornamental freshwater fishes from pet stores in Klang Valley, Malaysia - Nature
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OPEN Species composition and invasion
risks of alien ornamental
freshwater fishes from pet stores
in Klang Valley, Malaysia
Abdulwakil Olawale Saba1,2, Ahmad Ismail1, Syaizwan Zahmir Zulkifli1,
Muhammad Rasul Abdullah Halim3, Noor Azrizal Abdul Wahid4 &
Mohammad Noor Azmai Amal1*
The ornamental fish trade has been considered as one of the most important routes of invasive
alien fish introduction into native freshwater ecosystems. Therefore, the species composition
and invasion risks of fish species from 60 freshwater fish pet stores in Klang Valley, Malaysia were
studied. A checklist of taxa belonging to 18 orders, 53 families, and 251 species of alien fishes was
documented. Fish Invasiveness Screening Test (FIST) showed that seven (30.43%), eight (34.78%)
and eight (34.78%) species were considered to be high, medium and low invasion risks, respectively.
After the calibration of the Fish Invasiveness Screening Kit (FISK) v2 using the Receiver Operating
Characteristics, a threshold value of 17 for distinguishing between invasive and non-invasive fishes
was identified. As a result, nine species (39.13%) were of high invasion risk. In this study, we found
that non-native fishes dominated (85.66%) the freshwater ornamental trade in Klang Valley, while
FISK is a more robust tool in assessing the risk of invasion, and for the most part, its outcome was
commensurate with FIST. This study, for the first time, revealed the number of high-risk ornamental
fish species that give an awareness of possible future invasion if unmonitored in Klang Valley,
Malaysia.
As a global hobby, fishkeeping is cherished by both young and old people. Besides, it contributes to the improve-
ment of human well-being by building responsibility in children, managing stress in adults, and helping the
elderly to cope with their critical physical and psychological s tates1. However, some hobbyists lack information
or are careless regarding the preservation of natural b iodiversity2. When aquarium fishes attain large unman-
ageable sizes or become very aggressive, they are likely to be dumped into local w aters3. Hobbyists may also get
tired of certain fishes or get uncomfortable with their excessive breeding h abits4. This route of introduction is
probably the least regulated in many countries5. As a result, many fish species have deliberately or inadvertently
been introduced into the native ecosystems especially in areas where the aquarium fish industry is very active.
Therefore, the rate of introduction and spread of alien fish species has been eased by human activities and the
impacts are on environmental and/or s ocioeconomic1.
In Malaysia, aquarium trade stands as the second most important route through which alien fish species are
introduced into inland water bodies, after aquaculture6. From 2007 to 2014, the trade bloomed from the value
of USD 18.9 million to US 85.0 million in the country, indicating the importance of the industry7,8. However,
a larger proportion of the ornamental fishes in the aquarium business are alien, thereby increasing the prob-
ability of dumping, and risk of i nvasion6. In terms of propagule pressure, the aquarium route may out-perform
aquaculture as a pathway of species invasion if the dumping of unwanted aquarium fishes continues to increase
with minimal or no regulation and control9. Moreover, in countries like Japan, Singapore, Taiwan, and Australia,
dumping of ornamental fishes has been the main route of species introduction2.
Risk evaluation is essential as a first step in evaluating the hazard of alien species to the native ecosystem
and species biodiversity10. Consequently, different risk assessment methods have been developed and used to
1
Department of Biology, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor,
Malaysia. 2School of Agriculture, Lagos State University, Epe Campus, Epe 106101, Lagos, Nigeria. 3School of
Biological Sciences, Universiti Sains Malaysia, 11800 Gelugor, Penang, Malaysia. 4Institute of Advanced Studies,
University of Malaya, 50603 Kuala Lumpur, Malaysia. *email: mnamal@upm.edu.my
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understand and predict the invasiveness of alien fish species around the world including the Fish Invasiveness
Screening Test (FIST)2,11, Fish Invasiveness Screening Kit (FISK)12–15, and Aquatic Species Invasiveness Screen-
ing Kit (AS-ISK)16,17. Paradoxically, there is no single study on the invasion risk of alien ornamental freshwater
fishes in Malaysia using any of these tools. Since prevention has been identified as the backbone of alien invasive
species management, it is necessary to identify and understand the existing or potential risks of various routes
of aquatic species i nvasion18.
Being the most developed and populated region in the country, this research aims not only to identify the
ornamental fishes in pet stores, but also to ascertain the invasion risks of top aliens present in stores within
Klang Valley, Malaysia. This area is well known to harbour many ornamental fish pet stores coupled with its
sport fishing activities. Besides, highly populated areas are more prone to fish introduction19. The area is also
home to several local freshwater bodies including rivers, lakes, and streams that are susceptible to the dumping
of aquarium fishes. Moreover, this study will not only provide baseline information for future research, but also
serve as a tool for a more focused and intensified effort towards the management of alien fish species, and in the
long run, help prevent adverse impacts of fish species invasion in the local ecosystems.
Methods
Ethics statement. The fishes were sampled, handled, and sacrificed according to the methods approved
by Institutional Animal Care and Use Committee, Universiti Putra Malaysia. All methods were carried out in
accordance with relevant guidelines and regulations.
Study area. Klang Valley is situated at the centre of the west coast of Peninsular Malaysia and covers five
major areas such as the Federal Territory of Kuala Lumpur, Gombak, Hulu Langat, Klang and Petaling, where
they cover an approximate area of 2,832 k m2. The region cuts across cities such as Ampang Jaya, Kuala Lum-
pur, Klang, Petaling Jaya, Shah Alam, and Subang Jaya20. This area was selected as a result of being urban-
ized and with a heavy population of over 4 million people which represents about 16% of the entire country’s
population21. To see the spread and frequency of the various species in pet stores around the area, only retail
stores were included in the study. Likewise, the retail stores are more widely distributed and probably serve as the
major route through which alien fish species may be introduced into nearby local water bodies. The study took
place throughout the year 2019 and essentially surveyed all identified and accessible ornamental fish pet stores
within Klang Valley, Malaysia.
Sampling procedures. Since there was no official sampling frame to determine the total number of stores
within the sampling area, this study relied on the data from Department of Fisheries, Malaysia, and Google
maps to collate and locate all available pet stores in the area. The stores were screened for possible inclusion or
exclusion from the survey, after each visit. Pet stores that had too few freshwater fishes, usually just for display
purposes and those that deal only with marine fishes were also excluded from the survey. In each pet store, all
available fish species were observed and documented by listing the common and scientific names. Species that
could not be identified immediately were purchased and taken to the laboratory for further identification.
Species identification and checklists. The fishes were identified using a combination of keys and pub-
lications from previous studies22–28. Information on the order, family, species, conservation status, native distri-
bution, climatic zone, and the threat to humans were ascertained using FishBase29 and Eschmeyer’s Catalog of
Fishes30. Each species was designated as alien or native based on information gathered. However, identification
challenges were experienced with a few fish samples and so were not included for further analysis to avoid
misidentifications and erroneous conclusions. Eventually, checklists of all recorded alien and native fishes were
presented.
Descriptive analyses. Descriptive analyses were carried out using Microsoft Excel (Office 365, Version
2016, Microsoft Corp., Berkshire, UK) to present the charts and graphs showing occurrence frequencies and
other descriptive information about the recorded native and alien fish species. These include information
regarding families, orders, geographical origin, conservation status, native distribution, climatic zone, and the
threat to humans. To facilitate the analysis, all recorded fish species, after identification, were listed and each was
coded for each aquarium shop as 0 if the fish species was unavailable, and 1 for available fish species. Varieties of
any particular species were taken as a single species to avoid taxonomic confusion.
Percentage of occurrence, conservation status, climatic zone and the threat to
human. Recorded alien fish species were distinguished and classified based on the percentage of occurrence
(popularity) as low (≤ 25%), moderate (26—50%), and high (≥ 51—100%). Also, following previous s tudy31 and
using information from F ishBase29, the recorded information was detailed as follows: native range (continents
and sub-continents), basic climatic zones (temperate, tropical, sub-tropical), conservation status (such as not
assessed (NA), critically endangered (CR), near threatened (NT), least concern (LC), vulnerable (VU), data
deficient (DD))32 and potential threats to humans such as harmless (H), toxic (T), venomous (V), traumatogenic
(TR) and poisonous (P)29.
Comparison of fish occurrence by origin. The Mann Whitney U test was used to compare the occur-
rence of native versus alien fishes in the stores, while Spearman rank correlation was also carried out to identify
the strength, direction, and significance of the relationship between the number of alien fish species recorded
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No Traits Criteria Score
20.0 to 40.0 cm +
1 Maximum adult length 40.1 to 60.0 cm + +
> 60.0 cm + + +
0.0 to 10.0% +
2 Relative frequency 10.1 to 30.0% + +
30.1 to 100.0% + + +
0 to 7 countries +
3 History of establishment 8 to 15 countries + +
> 15 countries + + +
Low +
4 Ability to breed in the wild Moderate + +
High + + +
Low/Absent +
5 Competition with native species Moderate + +
High + + +
Specialist/not voracious +
6 Feeding plasticity Opportunist/moderately voracious + +
Generalist/voracious + + +
Low +
7 Temperature tolerance Moderate + +
High + + +
Low +
8 Tolerance to low dissolved oxygen Moderate + +
High + + +
Table 1. Scoring criteria for Fish Invasiveness Screening Test.
and the total number of species recorded in the pet stores using IBM SPSS Statistics for Windows, Version 23.0.
Armonk, NY, USA. These were done after exploring the data and confirming that they did not satisfy the condi-
tions for parametric statistical analyses.
Risk assessment. Risk assessment to quantify the invasiveness of the alien fish species was carried out. In
the first stage, the criteria for selection of recorded fish species which were included in the assessment are; per-
centage of occurrence greater than 25% in the sampled pet stores/existing history of establishment, percentage
of occurrence less than 25% in the stores/ previous reports of the species presence in Malaysian water bodies,
and percentage of occurrence less than 25% in the stores/evidence that the species has been established in many
other countries.
Secondly, the invasion risk was explored in two phases. First, using the Fish Invasiveness Screening Test
(FIST)2,11 with minor modification. Thereafter, the Fish Invasiveness Screening Kit (FISK) v2 was applied33. FIST
serves as a rapid tool that presents an index for screening latent biological characteristics associated with inva-
sion. For this study, characteristics considered include maximum adult length, propagule pressure (expressed
as % of occurrence frequency of a species in surveyed pet stores), history of establishment, breeding in the wild,
competition with native species, diet plasticity, temperature tolerance, and tolerance to low dissolved oxygen.
After ascertaining the characteristics of a species from consulted sources, the traits were classified as absent
or low ( +), moderate (+ +), and high (+ + +) for each species based on the eight considered f eatures2,11,25,34–43.
For computation, only a criterion where a species qualifies for ‘ + + + ’ is quantified using the ‘number 1′, while
a score below that such as ‘ + + ’ or ‘ + ’ is assigned a score of ‘0′ since they are not considered in the final risk
analysis2,11. The scoring criteria for FIST are shown in Table 1.
The percentage value of the Frequency Distribution (FD%) for screened criteria was enumerated for each
species after which invasiveness was measured from the calculated FD% value based on risk level. When a spe-
cies is with an FD% value for ‘ + + + ’ of above 50% for all screened criteria, they were classified as high-risk,
while species with values between 30 and 50% were classified as moderate-risk and those below 30% as low-risk.
Using FISK, species were analysed to double-check and ascertain the level of risk from FIST. The FISK is a
tool that evaluates invasion risk of fish species based on a set of 49 questions that fall into two groups such as
‘biogeography/history’ and ‘biology/ecology’, each having three and five subcategories, respectively4,33. Since
every response in FISK for each species has a certainty score (1 = very uncertain; 2 = mostly uncertain; 3 = mostly
certain; 4 = very certain) for each species, a ‘certainty factor’ (CF) was computed as ∑(CQi)/(4 × 49) (i = 1, …,
49), where CQi is the certainty for the question i, 4 is the maximum achievable value for certainty (i.e. ‘very
certain’) and 49 is the total number of questions in the FISK tool. The CF, therefore, ranges from a minimum
of 0.25 for all 49 questions with certainty score equal to 1 to a maximum of 1 for all 49 questions with certainty
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score equal to 4. In addition to the published literature consulted, databases such as the Database of Introduced
Aquatic Species (DIAS) (https://www.fao.org/fisher y/dias/en), Global Invasive Species Database (GISD) (https
://www.iucngi sd.org/gisd/), Centre for Agriculture and Bioscience International (CABI) (https: //www.cabi.org/),
FishBase (https://www.fishbase.org) and the United States Fish and Wildlife Service (USFWS) (www.usfws.gov)
provided information were used to complete the analysis.
The power of FISK v2 to correctly discriminate between non-invasive (low and medium-risk) and invasive
(high-risk) species gives a measure of its predictive potential44. Therefore, FISK was calibrated for Peninsular
Malaysia using the ROC (Receiver Operating Characteristics) after generating reports of 23 s pecies15,44. To
achieve this, a priori species categorization based on perceived invasiveness (i.e. invasive or non-invasive) was
carried out using information available from the Invasive Species Specialist Group database (ISSG) (http://www.
iucngisd.org/gisd/) and FishBase12,29,44–46. ISSG provides information on the establishment status of fishes in
non-native regions and gives general information on their ecology, distribution, impact, and management. For
the hybrid fish, a priori risk ranking was based on the taxon with the highest invasiveness risk44.
The ROC analysis presents a curve which is a graph of sensitivity versus 1- specificity (sensitivity versus
specificity). Here, sensitivity refers to the proportion of invasive and non-invasive fish species, respectively, that
are accurately recognized by the FISK tool. The area under the curve (AUC) helps to determine the precision
of the calibration analysis. An AUC of 1.0 means that the test is completely accurate and both sensitivity and
specificity are equal to 1.0 with no false positives (i.e. non-invasive species categorised as invasive) or false nega-
tives (i.e. invasive species categorised as non-invasive). Contrarily, an AUC of 0.5 means that the test is 100%
inaccurate and is unable to separate true positives (i.e. actual invasive species) from true negatives (i.e. actual
non-invasive species)14,44.
Assessments were carried out by two assessors (fish ecologists) leading to individual and universal ROC
curves. The universal ROC curve was computed using the mean scores from both assessors. From the global
ROC curve, the best threshold (cut-off) value that maximises the true positive rate (true invasive categorized as
invasive) and minimises the false-positive rate (true non-invasive categorized as invasive) was ascertained using
Youden’s J statistic47 and the closest point to the top-left part of the plot with perfect sensitivity or specificity45,48,49.
A ‘delta’ value was computed to determine the difference between scores obtained by both assessors44. Also,
the CFs for the 23 species were compared for the two assessors using the Mann Whitney U test15. All statistical
analysis was performed using IBM SPSS Statistics for Windows, Version 23.0. Armonk, NY, USA.
Results
A total of 60 ornamental fish stores located within the five districts that cut across Klang Valley area were suc-
cessfully surveyed (Fig. 1).
Species checklist, orders, and families. Checklists of all recorded alien (85.66%, n = 251) and native
(14.33%, n = 42) fish species are presented in Appendix 1 and Appendix 2, respectively. Species with no official
common names were considered as not available (NA) and the list was arranged based on families. The alien
fishes belong to 18 orders including Gymnotiformes, Acanthuriformes, Acipenseriformes, Anabantiformes,
Centrarchiformes, Cichliformes, Lepisosteiformes, Myliobatiformes, Osteoglossiformes, Atheriniformes,
Gobiiformes, Tetraodontiformes, Cyprinodontiformes, Polypteriformes, Cypriniformes, Characiformes, Silu-
riformes, and Perciformes. Most of them belong to the order Cichliformes (28.2%, n = 71) followed by Siluri-
formes (18.7%, n = 47) and Characiformes (15.9%, n = 40), while Perciformes, Gymnotiformes, Gobiiformes and
Centrarchiformes recorded the least number of species (0.40%, n = 1), respectively.
Out of the total of 53 families recorded, Cichlidae (n = 71) which belongs to the order Cichliformes and occu-
pied 100% of all Cichliformes recorded, followed by family Cyprinidae (n = 25) which occupied about 67.6% of
all Cypriniformes (Fig. 2). A total of 29 families had only one species each and these include Acipenseridae, Ana-
bantidae, Apteronotidae, Arapaimidae, Ariidae, Bryconidae, Centrarchidae, Chalceidae, Channidae, Clariidae,
Claroteidae, Cobitidae, Ctenoluciidae, Cynodontidae, Distichodontidae, Gasteropelecidae, Gastromyzontidae,
Gobiidae, Gyrinocheilidae, Hepsetidae, Monodactylidae, Mormyridae, Pangasiidae, Polyodontidae, Prochilo-
dontidae, Procatopodidae, Siluridae, and Tanichthyidae.
Percentage of occurrence and natural distribution. Based on percentage of occurrence (popular-
ity) at the 60 pet stores, only 4% (n = 11) of the alien fishes had high occurrence, 8% (n = 19) occurred moder-
ately, while the remaining 89% (n = 221) had low occurrence. The top occurring species with percentage occur-
rence > 25% included two-hybrid cichlids that had popularity (occurrence percentage) greater than 50% with
goldfish (Carassius auratus) having the highest popularity of 83.3% occurrence, while silver dollar (Metynnis
hypsauchen) had the lowest with the popularity of 26.7% occurrence (Appendix 1). The largest percentage of
alien fish species recorded in fish pet stores originated from South America (44%), followed by Asia (25%) and
Africa (20%).
Climatic zone, conservation status and the threat to human. A total of 91% (n = 228) of the
recorded fish species belong to the tropical climatic zone, while 8% (n = 21) and 1% (n = 2) belong to the sub-
tropical and temperate regions, respectively. Based on the IUCN Red List conservation status, 3% (n = 7) each of
the recorded species are endangered (EN) and near threatened (NT), while 4% (n = 11) and 1% (n = 4) are vul-
nerable (VU) and critically endangered (CR), respectively. Menarambo cichlid (Paretroplus menarambo), main-
gano (Pseudotropheus cyaneorhabdos), giant barb (Catlocarpio siamensis) and Siamese tiger perch (Datnioides
pulcher) were designated as critically endangered, while shovel nose tiger catfish (Pseudoplatystoma magdalenia-
tum), zebra loach (Botia striata), putitor masheer (Tor putitora), lipstick goby (Sicyopus jonklaasi), Boseman’s
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Figure 1. The administrative districts of the surveyed ornamental fish stores within Klang Valley, Malaysia.
To generate this figure, the shapefile containing administrative zones of Malaysia was sourced from DIVA-GIS
(http://www.diva-gis.org/gdata) and imported into ArcGIS Desktop version 10.2 (https://desktop.arcgis.com/en/
arcmap).
rainbowfish (Melanotaenia boesemani), Denison’s barb (Sahyadria denisonii) and striped catfish (Pangasianodon
hypophthalmus) are endangered, while elongate mbuna (Chindongo elongatus), emperor cichlid (Aulonocara
nyassae), silver carp (Hypophthalmichthys molitrix), panda cory (Corydoras panda), Blyth’s loach (Syncrossus
berdmorei) and royal knifefish (Chitala blanci) are near threatened. Interestingly, 5% (n = 13) of all alien fishes
were recorded as potential pests including species such as north African catfish (Clarias gariepinus), vermicu-
lated sailfin catfish (Pterygoplichthys disjunctivus), goldfish (Carassius auratus), common carp (Cyprinus carpio)
among others29. Only 2% of the species (n = 4) are traumatogenic29 (Fig. 3).
Species comparison in stores by origin. Non-native fish species were significantly (U = 159.0, p < 0.001)
higher in number (Mdn = 25) compared to the native fish species (Mdn = 6). Besides, Spearman rank correlation
indicated a significant positive association between the number of non-native fish and the total number of fish
species (r = 0.969, p < 0.001) recorded in the pet stores.
Invasiveness screening using FIST and FISK. Based on the selection criteria, the top 23 alien species
including 16 of the most occurring (> 25%) species and seven other species that satisfy the selection criteria were
subjected to invasiveness screening. FIST showed that seven (30.43%), eight (34.78%) and eight (34.78%) spe-
cies were considered to be of high, medium and low invasion risks, respectively. The high-risk species include
north African catfish (Clarias gariepinus), goldfish (Carassius auratus), common carp (Cyprinus carpio), guppy
(Poecilia reticulata), flowerhorn (cichlid hybrid), redtail catfish (Phractocephalus hemioliopterus) and sucker-
mouth catfish (Hypostomus plecostomus) (Table 2).
To calibrate FISK, AUCs (0.938, 1.000–0.840 CI for Assessor 1 and 0.929, 1.000–0.819 CI for Assessor 2)
from the ROCs were close for both assessors. As a result, an overall ROC was computed using the mean FISK
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Figure 2. Alien fish families encountered in ornamental fish pet shops within Klang Valley with number of
species in each family.
Figure 3. (A) Climatic zone of alien fish species; (B) IUCN Red List conservation status of recorded alien fish
species where NE = not evaluated, CR = critically endangered, NT= near threatened, LC = least concern, VU
= vulnerable, DD = data deficient, and EN = endangered fish species; (C) Recorded alien fish species and their
level of threat to humans; NA = not applicable. This figure was generated using Microsoft Excel (Office 365,
Version 2016, Microsoft Corp., Berkshire, UK).
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Invasiveness screening criteria
Species assessed 1 2 3 4 5 6 7 8 Invasion risk (%FD)
Poecilia latipinna + + + + + + + + + + + + Low (12.50)
Gymnocorymbus ternetzi + + + + + + + + + + Low (12.50)
Danio rerio + + + + + + + + + + Low (12.50)
Betta splendens + + + + + + + + + + Low (12.50)
Trichogaster lalius + + + + + + + + + + Low (12.50)
Pethia conchonius + + + + + + + + + + + Low (12.50)
Barbonymus gonionotus + + + + + + + + + + + + + + Low (25.00)
Piaractus brachypomus + + + + + + + + + + + + + + Low (25.00)
Pangasianodon hypophthalmus + + + + + + + + + + + + + + + Medium (37.50)
Pterygoplichthys pardalis + + + + + + + + + + + + + + + + + Medium (37.50)
Pygocentrus nattereri + + + + + + + + + + + + + + + + + Medium (37.50)
Puntigrus tetrazona + + + + + + + + + + + + + + Medium (37.50)
Astronotus ocellatus + + + + + + + + + + + + + + + + + + Medium (50.00)
Pterygoplichthys disjunctivus + + + + + + + + + + + + + + + + + + Medium (50.00)
Arapaima gigas + + + + + + + + + + + + + + + + + + Medium (50.00)
Cichla ocellaris + + + + + + + + + + + + + + + + + + + Medium (50.00)
Poecilia reticulata + + + + + + + + + + + + + + + + + + + + High (62.50)
Cichlid hybrid (flowerhorn) + + + + + + + + + + + + + + + + + + + + High (62.50)
Phractocephalus hemioliopterus + + + + + + + + + + + + + + + + + + + High (62.50)
Hypostomus plecostomus + + + + + + + + + + + + + + + + + + + + + High (62.50)
Cyprinus carpio + + + + + + + + + + + + + + + + + + + + + + High (75.00)
Carassius auratus + + + + + + + + + + + + + + + + + + + + + + + High (87.50)
Clarias gariepinus + + + + + + + + + + + + + + + + + + + + + + + High (87.50)
Table 2. Outcome of Fish Invasiveness Screening Test for selected top alien fishes from ornamental pet stores
within Klang Valley, Malaysia. % FD = frequency distribution (%) for (+ + +) score, low-risk = < 30%, moderate-
risk = 30 to 50%, high-risk = > 50.1% 1: Maximum adult length (cm), 2: Occurrence frequency, 3: History of
establishment, 4: Breeding in the wild, 5: Competition with native species, 6: Diet plasticity, 7: Temperature
tolerance, 8: Low dissolved oxygen tolerance.
v2 scores and this gave an AUC value of 0.938, 1.00–0.839 (Fig. 4). This indicates the ability of FISK to discrimi-
nate between invasive and non-invasive species based a priori classification. The best threshold as provided by
Youden’s J was chosen to be 17, which was the score used to calibrate FISK to distinguish between medium and
high-risk species. Because this threshold resulted in no invasive species being ranked as low risk, we retained
the FISK v2 score interval from -15 to 0 for low-risk species.
The obtained mean FISK scores resulted in 14 (60.9%) species classified as medium risk and 9 (39.1%) species
as high risk. The a priori classification gave 8 (34.8%) species as invasive and 15 (65.2%) species as non-invasive.
Out of the 15 species classified a priori as non-invasive, FISK was able to correctly classify 93.3% as medium-risk
and out of the 8 species, a priori classified as invasive FISK assessment was able to classify 87.5% as high-risk.
Furthermore, FISK scores for the 15 species a priori classified as non-invasive ranged from 6.5 to 24, while the
8 species a priori classified as invasive ranged from 14 to 32.5. Individual assessor scores ranged from 5 for ara-
paima (Arapaima gigas) to 36 for north African catfish (Clarias gariepinus), while the mean assessor scores ranged
from 6.5 for redtail catfish (Phractocephalus hemioliopterus) to 32.5 for north African catfish (Clarias gariepinus)
(Table 3). Five species including redtail catfish (Phractocephalus hemioliopterus), arapaima (Arapaima gigas),
red piranha (Pygocentrus nattereri), black tetra (Gymnocorymbus ternetzi) and flowerhorn (cichlid hybrid) had
the lowest FISK scores, while peacock bass (Cichla ocellaris), goldfish (Carassius auratus), amazon sailfin catfish
(Pterygoplichthys pardalis), common carp (Cyprinus carpio) and north African catfish (Clarias gariepinus) had
the highest FISK scores in ascending order.
Delta scores ranged from 1 to 7 and there was a significant negative relationship (p < 0.05) with mean FISK
scores (Fig. 5). The average CF for all responses (mean ± SE) was 0.87 ± 0.008.
Discussion
A vast majority of the alien species recorded in this study originate from the tropics, in line with the scenario
reported in Greece, Brazil, Canada, and U SA1,4,31,50,51. This trend signals that many species from that region
are of desirable ornamental characteristics possessing the ability to survive and thrive at least in a controlled
environment. Furthermore, Malaysia falls within the tropical region, and the high proportion of tropical alien
aquarium fishes recorded in this study signals the possibility of establishment since the environment may be
very suitable. Moreover, over a half (51%) and a third (35%) of the cichlid species originate from South America
and Africa, which are the first and third in terms of origin for species reported in this study, respectively. South
America has the most diverse fish fauna on earth which currently numbers over 9000 of freshwater and marine
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Figure 4. (A) Individual receiver operating characteristics (ROC) curves. (B) Mean receiver operating
characteristics curves for two assessors on 23 freshwater aquarium fish species in Klang Valley, Malaysia using
FISK.
FISK score CF
Species name Common name Mean ± SE Mean ± SE Invasiveness
Clarias gariepinus North African Catfish 32.5 ± 3.5 0.825 ± 0.015 High
Cyprinus carpio Carp 32.0 ± 2.0 0.825 ± 0.035 High
Carassius auratus Goldfish 26.0 ± 2.0 0.825 ± 0.025 High
Pterygoplichthys pardalis Amazon sailfin catfish 26.0 ± 3.0 0.905 ± 0.025 High
Cichla ocellaris Peacock bass 25.0 ± 2.0 0.935 ± 0.025 High
Hypostomus plecostomus Suckermouth catfish 24.0 ± 1.0 0.830 ± 0.020 High
Pterygoplichthys disjunctivus Vermiculated sailfin catfish 24.0 ± 1.0 0.935 ± 0.015 High
Astronotus ocellatus Oscar 21.0 ± 1.0 0.910 ± 0.020 High
Poecilia reticulata Guppy 19.0 ± 1.0 0.850 ± 0.030 High
Pangasianodon hypophthalmus Striped catfish 15.0 ± 1.0 0.855 ± 0.015 Medium
Barbonymus gonionotus Silver barb 15.0 ± 2.0 0.880 ± 0.000 Medium
Piaractus brachypomus Pirapitinga 14.5 ± 0.5 0.880 ± 0.010 Medium
Poecilia latipinna Molly 14.0 ± 1.0 0.890 ± 0.010 Medium
Betta splendens Siamese fighting fish 13.5 ± 0.5 0.845 ± 0.025 Medium
Danio rerio Zebrafish 13.0 ± 1.0 0.880 ± 0.010 Medium
Pethia conchonius Rosy barb 11.5 ± 1.5 0.865 ± 0.015 Medium
Trichogaster lalius Moonling gourami 10.0 ± 1.0 0.840 ± 0.040 Medium
Puntigrus tetrazona Sumatra barb 8.5 ± 2.5 0.890 ± 0.010 Medium
Pygocentrus nattereri Red piranha 8.0 ± 2.0 0.875 ± 0.035 Medium
Gymnocorymbus ternetzi Black tetra 8.0 ± 1.0 0.860 ± 0.020 Medium
Cichlid hybrid Flowerhorn 8.0 ± 1.0 0.830 ± 0.010 Medium
Arapaima gigas Arapaima 7.0 ± 2.0 0.935 ± 0.015 Medium
Phractocephalus hemioliopterus Redtail catfish 6.5 ± 1.5 0.795 ± 0.005 Medium
Table 3. Fish species assessed with FISK v2 for ornamental fish species within Klang Valley, Malaysia. High-
risk species were selected based on a threshold value of ≥ 17.
species combined, about 27% of all fishes around the world52. This huge number of species is likely to consist
of a correspondingly high number of freshwater ornamental fish species. This possibly explains the reason why
most of the species encountered originate from South America.
Furthermore, family Cichlidae probably consists of species with more desirable ornamental characteristics
compared to family Cyprinidae. This finding is in agreement with a previous s tudy31. However, it is slightly
different from the report of Magalhães and J acobi51 who reported Cyprinidae as the most popular, followed by
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Figure 5. Relationship between mean FISK v2 scores and the assessor difference (delta values).
Poeciliidae. Besides, all of the alien cyprinid fishes recorded in pet stores originate from other Asian countries.
This gives an idea of the abundance of cyprinids in the region and the risk of further introduction of new species.
The proximity of Malaysia to other Asian countries could also facilitate this situation since importation from
these countries would likely be easier compared to countries in farther continents.
Occurrence frequency may likely predict the magnitude of release (propagule pressure) of alien fish into
native ecosystems3. For example, Duggan et al.9 in their study of ornamental fish species available in Canada and
the USA established a relationship between the occurrence frequency of alien fish families in stores and their
subsequent introduction and establishment. Goldfish (Carassius auratus), freshwater angelfish (Pterophyllum
scalare) and Sumatra barb (Puntigrus tetrazona) were the most occurring alien fishes in this study. This, in part,
is similar to the findings in Pacific Northwest that cuts across USA and C anada1, and for San Francisco Bay-Delta
region in California, USA4,53. A previous report with an even higher frequency of occurrence is probably due to
the broader coverage of that s tudy3.
This study also indicates that alien fish species contributed the most to the total number of species avail-
able for sale. Although chain stores were not encountered during the survey, previous studies have noted that
independent retail stores generally sold a higher number of different fish species compared to chain s tores54.
Alien fish species have been recorded from diverse ecosystems in Malaysia, and these include, but not limited
to drainage areas, mining pools, lakes, reservoirs, swamps, streams, and rivers6,55–57. The presence of some of
these species including peacock bass (Cichla ocellaris), striped catfish (Pangasianodon hypophthlamus), piranha
(Serrasalmus sp.), arapaima (Arapaima gigas), north African catfish (Clarias gariepinus) and tilapia (Oreochromis
spp.) has been attributed to purposeful introduction into local waters6,58. Besides, some of them are well adapted
to the environment, grow rapidly, feed on local fishes, and some are considered invasive59,60. For example, the
Amazon sailfin catfish (Pterygoplichthys pardalis) has established a self-breeding population in Langat River,
Selangor, and more than 10 tonnes of the fish were reportedly been caught from the Skudai River, Johor. They
may have outcompeted the native fish species owing to their hardy c haracteristics61,62. This species also disrupt
the environment since they dig the river bottom to make burrows to lay eggs. As a result, they tend to contribute
to erosion and sedimentation of the river b ottom63.
As one of the top-ten countries that produce ornamental fishes of freshwater origin, the ornamental fish
industry in Malaysia is a sizeable one and includes the collection, breeding, and marketing which creates jobs
for the locals and generates foreign exchange for the country64–66. However, there are pieces of evidence that the
ornamental fish trade is a vital route through which alien fish gets introduced and t ranslocated4,50,67,68. In fact,
due to their behaviour and potential to attain large sizes, alien species belonging to the genera Hypostomus and
Pterygoplichthys likely get released especially when they become too large for most domestic a quaria3.
Just like in this study, FIST was earlier used for selected ornamental fish species in B razil2 and I ndia11.
However, a slight modification of their methods warranted the inclusion of occurrence frequency of alien fish
species as part of the criteria for risk analysis. This may be the reason why some known high-risk species turned
out to be of moderate-risk due to their low to moderate occurrence in the stores, which reduced their scores
during analysis. Some of the high to moderate-risk species are known to have established breeding popula-
tions in Malaysian inland waters. For example, the peacock bass (Cichla ocellaris), vermiculated sailfin catfish
(Pterygoplichthys disjunctivus), Amazon sailfin catfish (Pterygoplichthys pardalis), arapaima (Arapaima gigas),
alligator gar (Atractosteus spatula) and pirapitinga (Piaractus brachypomus) have been encountered in some
water bodies around the country21,61,62,69. The impacts of these and other medium to low-risk species on Malay-
sian freshwater ecosystems have probably not been extensively studied. Although most of the low-risk species
from FIST (medium risk species from FISK) are known to be small-sized, guppy (Poecilia reticulata) which is
also small-sized turned out to be of high-risk from both FIST and FISK. Furthermore, high-risk species like
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north African catfish (Clarias gariepinus) have been reported from native waters and recorded in aquaculture,
a purpose for which it was i ntroduced6.
Concerning high-risk species, both FIST and FISK gave similar outcomes by designating species such as
north African catfish (Clarias gariepinus), carp (Cyprinus carpio), goldfish (Carassius auratus) and suckermouth
catfish (Hypostomus plecostomus) as high-risk species. This shows that both tools are valuable, although, FISK v2
is likely more robust due to its higher number of questions, the inclusion of multiple elements that are considered
to be valuable in predicting potential invasion success through previous invasion history, establishment success
in other regions, climate matching and documented impacts70,71, and the ability to calibrate it for a specific risk
assessment area44,72,73. The success of FISK v2 to discriminate between invasive and non-invasive fish species
in this study is in line with earlier studies14,44,72,73. Besides, it has been suggested that before the application of
FISK, a rapid screening tool may be utilized to flag the potentially high-risk s pecies73. Therefore, FIST may be
considered as a first-stage rapid risk screening t ool11.
Despite being designated to be of high-risk, little or no reports regarding establishment in the wild exist for
species such as carp (Cyprinus carpio), goldfish (Carassius auratus) and oscar (Astronotus ocellatus) which also
turned out to be of high risk. This is probably due to failed introduction owing to biotic and abiotic influences44,74,
insufficient propagule pressure to guarantee the establishment of these species, or are yet to be detected in the
wild. These species, therefore, appear to pose no considerable risk of invasiveness in the risk analysis area. This
is similar to a report for some six high-risk species including goldfish and guppy in peninsular Florida, U SA44.
All of the low-risk species from FIST turned out to be of medium risk according to FISK. Besides, some spe-
cies known to have been established in local waters and of likely serious impact on biodiversity and environments
like Amazon sailfin catfish (Pterygoplichthys pardalis), vermiculated sailfin catfish (Pterygoplichthys disjunctivus)
and peacock bass (Cichla ocellaris) are of medium risk according to FIST and of high-risk according to FISK.
Again, this may be due to the robustness of FISK making it more accurate in designating the invasion status.
In this study, the calibrated high-risk threshold value of 17 is close to scores reported by previous studies rang-
ing from 17 to 23, as reported by those that applied FISK v145,75,76 and v212,13,46,77. Contrarily, it is quite higher than
the threshold values of 9.5, 11.75, and 10.5 from FISK v2 reported for the southern Balkan countries, northern
Balkan countries (Croatia and Slovenia) and Florida, USA, r espectively10,44,72. Moreover, the low range (3 to 7)
of delta values and the negative relationship between the delta values and mean FISK scores indicate that the
assessors generally have closer certainty levels for the species with higher scores than for the low scoring species.
This differs from the wide range and positive relationship reported for the FISK v2 assessment of fish species
from peninsular Florida, USA44. A possible reason for this is the higher number of assessors in their study which
may have given rise to more divergent opinions.
This study represents the first attempt to risk-screen alien ornamental fish species in Peninsular Malaysia.
We acknowledge the need for further studies to carry out screening of more species including those mainly
for aquaculture which were not captured in this study. Moreover, there is a need for improved monitoring
and management of the high-risk species where some of them are among the most popular ornamental fishes
traded all over the w orld3. Priority should be given to those with established breeding populations, while those
yet to establish should be prevented from getting introduced. In addition to the existing plan and efforts by
the Malaysian government through the Department of Fisheries, Ministry of Agriculture and Food Industries,
together with the Ministry of Energy and Natural Resources, aquarists and hobbyists should be involved as they
are valuable in the successful monitoring and management fish introduction and invasion3. In case of the need
to import new fish species in the future, an initial risk screening should be adopted to help hint on the possible
impacts and guide policy decisions.
Conclusion
Although noted as the second most important route for the introduction of alien fishes in Malaysia, the aquarium
trade, judging from its composition of numerous alien fish species, could overtake aquaculture as a source of
invasive fish introduction if these fishes continuously find their way into the local waters. The number of high-
risk ornamental fish species gives an idea of a possible future invasion if unmonitored. Moreover, FISK is most
likely a more robust tool in assessing the risk of invasion and for the most part, its outcome was commensurate
with that of FIST with some differences. This also shows the value of FIST for an initial and rapid application.
Received: 23 February 2020; Accepted: 25 September 2020
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